Third Generation Partnership Project (3GPP) and 3GPP2 are considering long term evolution (LTE) for radio interface and network architecture. Currently, receivers use a common reference signal for channel estimation, decide the precoding matrix based on the estimated common channel and feedback the information about the preceding matrix to the transmitter. The transmitter then uses the signaled precoding matrix and multiplies it with the data signal to be transmitted. Due to the feedback error the precoding matrix used by the transmitter may be different from the precoding matrix signaled from receiver. Also due to network flexibility, the transmitter may decide to use a different precoding matrix than the one that is signaled from receiver even if there is no feedback error. Therefore the information about the precoding matrix used by the transmitter has to be signaled to the receiver via control channel. The receiver is then able to decode the control channel to obtain the preceding information and use this precoding information to demodulate the precoded data signal.
Orthogonal frequency division multiplexing (OFDM) is a data transmission scheme where the data is split into smaller streams and each stream is transmitted using a sub-carrier with a smaller bandwidth than the total available transmission bandwidth. The efficiency of OFDM is a result of the fact that the sub-carriers are selected so that they are orthogonal to each other. In other words, the sub-carriers do not interfere with each other while each is carrying a portion of the total user data.
Multiple Input—Multiple Output Orthogonal Frequency Division Multiplexing (MIMO OFDM) and MIMO Single Carrier Frequency Division Multiplexing Access (SC-FDMA) are air interface technologies used for high data throughput (HT) services. Various forms of transmit beamforming are currently being considered for these technologies, including eigen-beamforming, spatial multiplexing, and space time coding. Each of these techniques, though, requires channel state information to be available at the transmitter in order to enable the maximum achievable capacity. Because the amount of information required for feedback may be excessive for a practical system, methods to reduce the amount of required feedback have been developed. Methods for reducing feedback include codebook methods, phase quantization methods, open loop methods including channel sounding, and statistical prefiltering.
Efficient signaling of precoding information or antenna weights from the transmitter (NodeB) to the receiver (UE) are essential to multiple-input multiple-output (MIMO) system for evolved universal terrestrial radio access (E-UTRA), especially for both SU and MU MIMO using precoding or beamforming.
As such a method and apparatus are needed to provide efficient communications between transmitter and receiver for precoding information and antenna weights and improved effective channel estimation at the receiver (or UE).